Solution is a homogeneous mixture of two or more substances.
A mixture is that form of matter in which two or more substances are present in any proportion.
Therefore, air is a mixture.Air is homogenous mixture but the propotions of nitrogen,oxygen,carbon dioxide and water vapour are not fixed exactly.The compositions of air differs from place to place and from time to time.So, it is a mixture.The properties of air are not different from those of its constituents.Various components of air can be separated by a simple process called fractional distillation.Therefore, air is a mixture.

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